1. Field of the Invention
The present invention relates in general to preventing a program, which has been transmitted through a computer communication network such as the Internet, from being illegally reproduced. More particularly, the invention relates to an apparatus and method for encrypting a digital data file in such a manner that the digital data file cannot be decrypted even if the encrypted data file is intercepted while being downloaded to a digital data player, and to an apparatus and method for decrypting the encrypted data files.
2. Description of the Related Art
MP3 (shorthand for MPEG-1 Layer 3 Audio) is one of various available digital data formats for audio data. An MP3 player is a new notional, portable digital device capable of readily downloading and reproducing desired data from a computer communication network using an audio data compression coding technique prescribed in MPEG-1 Layer 3. The MP3 player has few faults and excellent sound quality because it stores a file in the form of digital data. Further, the MP3 player is small in size and light in weight, thereby assuring high portability such that a user can carry it even during his physical exercise. For these reasons, this product is a viable alternative to a portable cassette tape recorder and compact disk (CD) player.
With reference to FIG. 1, there is shown in block form a conventional arrangement of a digital data player and associated peripheral devices. In this drawing, the reference numeral 10 denotes a digital data server which assigns an identification (ID) number and password (PWD) to a personal computer 20 for user registration, and which also transmits a digital data player 22 in software form to the personal computer 20. Upon receiving a file supply request from the user, the digital data server 10 identifies the user on the basis of an ID number and password entered by him and supplies an encrypted digital data file to the user in accordance with this identification. The personal computer 20 stores the digital data file supplied from the digital data server 10 on a hard disk 21 therein and decrypts it through the downloaded software player 22 to reproduce the resultant unencrypted digital data file or to download it to a digital data playing device 30. The digital data playing device 30 downloads the unencrypted data file from the personal computer 20 and stores it in a memory unit 40 for the reproduction thereof. The memory unit 40 downloads the unencrypted digital data file from the digital data playing device 30 and stores it in its internal memory 42 to output the file for a desired playing operation.
The operation of the conventional arrangement with the above-mentioned construction will now be described.
In order to legally receive a desired digital data file from the digital data server 10, the user has to register with a digital data file supplier. During user registration, the user is assigned with an ID number and password from the digital data file supplier. Then, the user downloads a digital data player 22 in software form from the digital data server 10 through a communication network and installs the downloaded digital data player 22 in the personal computer 20.
Thereafter, to download a desired digital data file from the digital data server 10 through the personal computer 20 and a communication network, the user transmits his ID number and password to the digital data server 10 through the personal computer 20 and communication network. The digital data server 10 identifies the user on the basis of the transmitted ID number and password and supplies the desired digital data file to the user in accordance with the identification. At this time, the digital data server 10 encrypts the digital data file using the user's ID number as an encryption key and transmits the encrypted digital data file to the personal computer 20.
The personal computer 20 stores the digital data file transmitted from the digital data server 10 on the hard disk 21. Then, upon receiving a reproduction request from the user, the personal computer 20 decrypts and reproduces the stored digital data file via the digital data software player 22. As a result, the user is able to listen to desired music through the personal computer 20.
On the other hand, if the user intends to listen to music in a digital data file form using the portable digital data playing device 30, then the personal computer 20 decrypts the digital data file, stored on the hard disk 21 with the digital data software player 22, and sends the decrypted digital data file to the digital data playing device 30 through a download unit 23 therein and a communication network.
Then, the digital data playing device 30 stores the digital data file, sent along the above path, in the memory 42 of the memory unit 40, which is typically in the form of a removable card. If the user requests the digital data player 30 to reproduce the digital data file stored in the memory 42, then the digital data player 30 reads the stored digital data file from the memory 42 and reproduces it through a decoder 32 therein. As a result, the user can listen to desired music anywhere using the digital data player 30.
However, the above-mentioned conventional arrangement has a disadvantage in that the digital data file may be intercepted from the communication network during downloading from the personal computer to the digital data playing device (or from the digital data playing device to the memory card) in an unencrypted condition. Such an interception of the unencrypted digital data file makes it impossible to protect the copyright of a music copyright holder and music copyright associates (for example, a music producer and planner taking charge of music production, duplication and distribution).